1. Field of the Invention
The present invention relates to a resin encapsulation mold. In particular, it refers to a resin encapsulation mold, which performs resin encapsulation for a chip-shaped semiconductor device that is mounted on a lead frame.
2. Description of the Prior Art
A chip-shaped semiconductor device mounted on a lead frame and having its electrode pads and leads of the lead frame wired are normally formed into a package body, which is an outer shell of resin and is encapsulated in resin using a resin encapsulation mold. In addition, current semiconductor devices tend to have packages having enlarged outer shells with thin walls, an increasing number of pins as outer leads, and ever narrowing pitch therebetween.
For such a semiconductor device, the resin encapsulation mold has had various suggested modifications come about such as regarding the velocity control of the ejection mechanism and clamping of the resin injection structure and/or the formed outer resin shell in order to prevent air bubbles, chips or cracks from developing in the outer resin shell used as the package body.
An example of semiconductor device fabrication equipment solving such problems is disclosed in Japanese Patent Application Laid-open No. Hei 11-87378. The resin encapsulation mold that is used as this semiconductor device fabrication equipment has a scale affixed to the lower mold and detects whether the position of the lower end of the scale is above a predetermined position or below it, and based upon the detection results, changes the speed at which the lower mold is dropped and reduces the load imposed on the semiconductor device during ejection of the semiconductor device from either the upper or lower mold in order to solve the problem of cracks or chips in the resin package body.
In addition, the load exerted during ejection by a load cell is detected, and if the amount detected is above a predetermined amount then a warning such as an alarm is given off, the equipment stops, and the residue on the mold is removed to solve the problems mentioned above that are due to residue being on the mold.
With the aforementioned semiconductor device fabrication equipment, while problems such as defects, cracks and breaks in the resin package body that develop during mold separation are able to be solved, the development of air bubbles near the injector pin during resin injection is unable to be avoided. In order to enclose a large semiconductor chip in a thin resin package, resin having low elasticity is used for injection so as not to impart damage to the wiring or interconnects. Alternatively, the resin injection speed is made exceedingly fast.
However, the injector pins that protrude from the inner walls of the cavity become an obstacle for the fast-flowing resin during the injection of resin from the gate. More specifically, as shown in FIG. 6, when the molten resin injected from the gate flows into cavity 6, the molten resin collides with ejection pin 7, a space develops near the shoulder-like portions of ejection pin 7, and this space becomes enveloped in the molten resin causing the problem of residual air bubbles.
In order prevent the development of such air bubbles, if the end surfaces of the ejector pins were to lay in the same plane as the inner walls of the cavity, then cavitation would not occur and leave behind air bubbles; however, even if the length of the ejection pins is precisely machined and they are accurately structured, the amount of protrusion of each ejection pin varies. For instance, supposing there are four ejection pins in each cavity, if there are eight cavities encapsulating a semiconductor device within the same mold, then there are a total of thirty-two ejection pins, which is a large number of pins. It is difficult to structure all of the ends of such ejection pins in the lower part of the indentation of the mold to lie in the same plane.
For example, even if the precision of the length of the ejection pins is machined to be within a few xcexcm and assembled, due to manufacturing errors occurring in the flatness of the material comprising the mold and the structural precision of the mold, the amount of protrusion of all of the ejection pins in the bottom of indentations 9 and 10 may vary within a range of 100 xcexcm or more. Even within the same cavity, the amount of protrusion may even be as much as 100 xcexcm.
Objects of the Invention
The objective of the present invention is to provide a resin encapsulation mold capable of encapsulating a semiconductor device in resin without having any air bubbles develop in the vicinity of ejection pins.
A resin encapsulation mold of the present invention comprises a lower mold, which is mounted on a lead frame, includes an indentation into which a semiconductor device is placed, and forms a gate through which resin is injected; an upper mold, in which an indentation is formed opposite the indentation of the lower mold to configure a cavity for holding the semiconductor device; a plurality of ejection pins, which protrude from the respective bottoms of the indentation of the upper mold and the indentation of the lower mold into a resin package body formed by injecting the resin from the gate into the cavity and eject the resin package body; a vertical drive mechanism, which brings into contact and separates the upper mold and the lower mold; and protrusion adjustment means for adjusting the amount of protrusion of the respective ends of the plurality of ejection pins protruding from the respective bottoms of the indentations of the lower mold and the upper mold comprising the cavity while resin is being injected into the cavity; wherein the amount of protrusion of the plurality of the ejection pins ranges between 0 and 60 xcexcm.